Telecommunication is effected with cellular telephony base station transmit-receive systems by (a) transmission signals propagated through space from the station and occupying a wide-band of frequencies and (b) reception signals propagated through space to the station and occupying a wide-band of frequencies different from that occupied by the wide-band transmission signals. Both the wide-band transmission signal and the wide-band reception signal are at RF frequencies and are subdivided into the same number X of smaller frequency bands which, although different in frequency, respectively correspond to each other one-to-one, and which respectively provide for the system X channels for conducting respective channel signals representing different conversations. In the use of the system, the smaller frequency "channel" bands in, respectively, the wide-band transmission and reception signals and corresponding to only one channel are occupied from time to time by, respectively, transmission channel signals and reception channel signals for that one channel.
In the case of wide-band reception signals, those signals may be of two kinds, namely, main wide-band reception signals, and diversity wide-band reception signals received by, respectively, a main antenna and a diversity antenna for the base station system. Both such main and diversity wide-band reception signals occupy the same wide frequency bands and differ from each other only in respect of the antennas by which they are received.
To restate the above, a base-station transmit-receive system utilizes X channels of which each channel is different in the frequency bands employed therefor from any other of such X channels, each of the X channels being provided by (a) a channel frequency band therefor within the wide-band transmission signal,. (b) a different channel frequency band therefor within the wide-band main reception signal, and (c) another channel frequency band therefor (the same in frequency as the mentioned channel band within the wide-band main reception signal) which is within a wide-band diversity reception signal in the event the system provides for diversity reception. As indicated above, "transmission channel signals" and "receiver channel signals" are signals which are contained within particular respective channel bands, and which convey conversations to be transmitted and received, respectively, by the base station. There may be two species of receiver channel signals, namely, "main receiver channels" and "diversity receiver channel signals".
Because of peculiarities in allocating frequencies for use in cellular telephony, the wide-band reception signal for any cellular telephony base station spans an interval in the frequency spectrum which includes, on the one hand, bands of frequencies allocated to that signal and containing the X channels therefore (and wanted receiver channel signals in those channels) and, on the other hand, a central band of frequencies interposed between those allocated bands, and containing receiver channel signals which are unwanted because they are likely to interfere with the wanted receiver channel signals. An initial step, therefore, in the processing of the received signals has been to filter the wide reception signal while at RF frequencies to attenuate signals and/or noise components in that central frequency band by a substantial degree and, preferably, down to a level at which they are incapable of producing significant interference with the wanted receiver channel signals. In the past, however, the filtering devices used to effect such filtering have been bulky and expensive.